Frequently, there is a need within a variety of process applications to provide a seal for a pressurized vessel. Such a seal must contain the pressurized fluid without leaking. In the case of a threaded connection this requirement dictates that the mechanical engagement connecting the seal to the pressurized vessel be tightened with a substantial amount of force, thus the torque applied to the connection must be relatively high in order to provide a fluid-tight seal within the threads themselves or to create a force which acts upon a seal. This is an undesirable situation, however, since reliance is placed upon an operator to sufficiently tighten the seal to the proper torque without overtightening, which may damage the components.
Thus, in an instrument in which a pressurized fluid (typically supercritical or near-critical fluids, gases or liquids) flows through a vessel containing a sample (solid, semi-solids, small quantities of liquids) it is currently necessary to install sample containment vessels which require manual tightening of end caps using wrenches to seal the vessel. A second step of incorporating the sealed containment vessel within the system also requires making connections to the rest of the components using tubing fittings which also must maintain a high pressure seal. Additionally, some systems immerse the vessel in a thermal zone--e.g., ovens, heater blocks. As pointed out above, wrench-tightening to achieve seals is awkward and imprecise, and can be unreliable; this applies to cap seals as well as to connector seals. Nor is wrench-tightening amenable to automation; immersion in thermal zones can require many manipulations in addition to making all sealing connections, e.g., opening and closing oven doors, manipulating latch mechanisms, and affixing heater blocks. Implementation of the thermal zone within a pressurized system utilizing a sample containment vessel can therefore be a barrier to automation.
It would therefore be desirable to assume responsibility for creating high pressure seals within an extraction instrument to assure reliability and safety. Further, it would also be desirable to automate the sealing process. In many systems it is also desirable to provide improved access, e.g., "z-axis" (vertical) entry for interfacing with robotic systems or future autosampling systems implemented for the instrument. In many systems requiring the insertion and removal of a pressurized sample containment vessel it is further desirable to provide a thermal zone which would foster, not inhibit, automation. The sample containment hardware provided would preferably be analogus to typical laboratory supplies (overall geometry and volume, hand-tightened caps) and allows automatic tracking of the sample by incorporating details allowing labeling or machine readable coding, such as bar coding. A complete seal formation system would also provide means for the detection of leaks from any of the seal areas when the chamber is closed, and would provide safety interlock protection from the high forces required to produce an automated sealing process.
It is also desirable to provide a pressurized portion within a process which permits pressurized fluid to flow through a region while a seal is maintained. However, this facet adds a greater degree of complexity to formation of a seal when conventional threaded seals are used. For example, in certain chemical analytical sample preparation apparatus, the fluids being contained must be in the supercritical fluid phase. This requirement dictates that the sample be subjected to the appropriate conditions of pressure and temperature which result in the supercritical fluid state. Due to the serial nature of sample preparation with quantitative chemical analysis, a reliable seal is required. Also, due to the usual repetitiveness with which such chemical analyses are performed, a reusable high pressure seal is required. It would thus be desirable in the operation of such systems to provide a more reliable, long-life seal mechanism and a system which would verify sealing and provide diagnostic information (e.g., presence of all the input hardware). Also, since analysis is usually performed to ascertain certain characteristics of the sample, it is important that at least a nominal seal be maintained to prevent sample contamination or loss, and thereby retain sample integrity during all phases of sample preparation or analysis.